The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Conventionally, a wheel-speed sensor is used for detecting the rotation speed of a vehicle's wheel by cooperating with a sensing metal ring. The wheel-speed sensor and the sensing metal ring usually are mounted near a brake disc of the vehicle. However, because wheel-speed sensor and the sensing metal ring are exposed to the external environment directly, the environmental impurities and liquid may affect the sensitivity of the wheel-speed sensor or aggravate aging of the wheel-speed sensor accordingly.